Cryjlah of OxldrJcd Tin Ore. i^y 



cations obferved on them, from which I have formed my 

 arrangement agreeably to the law laid down by Hany him- 

 felf, (fee Phil. Mag. Vol. I. p. 292.) I fee no reafon at 

 prefent why I fliould alter it. The cryftals of oxidated tin 

 are in general fo hard and brittle that I have not been able 

 to feparate the lamince ; and there is nothing to gnide the 

 obferver but the dircftion of the flrise on the fecondarv facets. 

 Now the faces, w-hich are parallel to the faces of the o<Staedrou 

 before mentioned, are always very brilliant ; but thofe which 

 are on a plane with the edges are ftriated parallel to thofs 

 edges, particularly thofe cryftals which fl^ew the interme- 

 diate ftages of the third law. If the nucleus were a cube, 

 and the laminae accumulated on it, to form the fecondary 

 cryftals, {liewed their direftion by ftriae on the new facets, 

 thofe ftriae would be in a direction quite contrary to what 

 are llicwn on thcfe cryftals : inftead of going the length of 

 the ne^v facets parallel to the edges of the oftaedron, thev 

 would crofs the facets perpendicularly to their prefent direc- 

 tioUj and it would be impoffible for the cryfl:al fig. 7 to 

 take the form of fig. 8. In my eolleftion there is a group 

 of opaque black crj'ftals, fhewing all the variations from the 

 primitive prifmatic cryftal fig. 2, to the completion of the 

 third law of decrement fig. 8. In all of them the direftion of 

 the ftrix is very evident. The Saxon and Bohemian ores of 

 tin are moft common in the cabinets of France : the cryftals 

 arc Lirger, but do not prefent the varieties of forms tliat 

 Englifh ores da; being moltly confined to the oftaedron and 

 its hemltrope, and thofe variaticais of the fourth law whicli 

 approach the cube. Had Hauy feen a greater number of 

 the varieties of the Englifli tin ores, I think he would, for the 

 primitive form, have had recourfe to the odlaedron, which, 

 by a very fiinple law of decrement, produces the cube ami 

 its varieties that occur in the tin cryftallifations. 



To thcfe obfcrvations may be added Do ITfle's defcripliou 

 of the fame cryftal'that Ilauy has dcfcribed (above), which 



I find 



